Hello Mewerner59,
Welcome to Apple Support Communities. We understand that your Apple Watch battery life isn’t as expected after pairing it to your iPhone 13. We are happy to help.
We appreciate the troubleshooting that you have done to this point. Please try the tips here: Batteries - Maximizing Performance - Apple
What is the exact watchOS installed on your Apple Watch? There was a recent watchOS update. We recommend the steps here of you haven’t updated: Update your Apple Watch - Apple Support
Let us know the results.
Take care.